There is inadequate information about the nature of the acetylcholine binding sites on postsynaptic membranes (AChR) and how the events initiated at these receptors are coupled to ionic, potential, biochemial and mechanical changes. Snake a-toxins bind with high affinity and nearly total specificity to AChR and they have been used as ligands in affinity chromatography to isolate the receptor protein from fish electric organs. This highly selective method appears to afford a reasonable route to the isolation of the AChR from a mammalian tissue. The principal neurotoxin of Naja naja siamensis will be purified, isotopically labeled with I125 and its extent of binding to specific regions of porcine brain and diaphragm will identify the tissue most suitable for isolation of the AChR. Detergents will be used to solubilize AChR from the tissue and crude receptor will be characterized to studying the effects of cholinergic agonists and antagonists, lipases, proteases, heat, detergents, etc. on the formation of the toxin-receptor complex. The conditions necessary to efficiently reverse this complex will be defined and AChR purification will follow by affinity chromatography with the neurotoxin as ligand. Purified AChR will be characterized kinetically (binding studies with muscarinic, nicotinic, and acetylcholinesterase inhibitors), chemically (amino acid composition and sequence, presence of carbohydrate or lipid), structurally (presence of alpha-helix, Beta-structure, sub-unit composition, allosteric properties, and functionally (reconstruction and study of synthetic "excitable" membrane prepared with lipid bilayers). Data from these studies will increase understanding of drug-receptor interactions thereby facilitating the choice and design of drugs for therapeutic purposes. Additionally, this research will potentially provide information on the general structure and function of membranes.